In general, commercially available gas laser tubes, such as the helium-neon lasers available from several manufacturers, are designed to produce a near collimated beam by shaping the last surface of the output mirror such that after refraction all "rays" are close-to-parallel with the axis of the laser cavity. In other words, the laser beam last exiting the surface of the tube produces a near-plane wavefront. However, a great majority of laser based optical systems require focusing of the collimated beam. The components required to accomplish this include a properly coated singlet lens, a precisely matched lens barrel, a mount for the lens barrel and a means for holding this assembly in a precise location with respect to the exiting laser beam. Highly skilled labor trained to use relatively sophisticated instruments for alignment of the laser/lens arrangement is also required.
According to the present invention, a technique is utilized for focusing the output beam from a laser at an appreciable optical distance from the laser optical cavity without intervening optical elements. The present invention provides a direct focused gas laser wherein the last surface of the output mirror, in the case of a laser where the mirrors are integral to the ends of the laser tube envelope, is shaped such that it produces a cone, or wedge, shaped beam with the required F/number. A spherical surface provides a cone-shaped beam whereas a cylindrical surface produces a wedge-shaped beam. In the case of Brewster type laser, the envelope-enclosing windows are correspondingly shaped. The economic advantage of utilizing this technique is apparent since it eliminates all material and labor normally required for focusing a laser beam and requires less volume for packing the laser in laser based optical systems.